I'm currently waiting for my number to be ported from my old network before I can actually use it as a phone (no reviews I've read actually review how it performs as one). In the meantime I've been playing around with the other stuff it does. The current likes and dislikes:

Likes

The screen is very nice - easily readable on 20% brightness, touch responsiveness is good. Probably not quite a smooth as the glassy iphone / ipod touch surface.

The size - smaller than an ipod touch. A lot thinner / smaller than the G1 from what I've seen.

On screen keyboard rotates with the screen - makes typing a bit easier.

Battery life - seems adequate for a device with this much crammed in. Turning off wifi overnight means the battery drops by only a couple of %.

The built in browser is a bit clunky - fit webpage to screen is badly implemented. Opera Mini doesn't seem to know about the onscreen keyboard in Android 1.5 yet and so is unusable.

No multi-touch due to Apple patents.

The mechanical rollerball a) feels like a deodorant bottle b) is not really needed and c) is just waiting to fill up with pocket fluff, etc.

Also managed to install ScummVM and now have The Curse of Monkey Island on my phone...

The IMAP email client seems to have improved since the G1 firmware but I still get connection errors every few minutes. I'll be interested to see what calling people and messaging them via SMS is like once the number gets ported.